The present invention relates to a method and device for welding an aluminum or aluminum alloy stud and, more specifically, to a welding method and device in which a stud is brought into contact with a base material, voltage is applied between the stud and the base material, the stud is lifted slightly off the base material, an arc is generated between the stud and the base material, the tip of the stud and the section of the base material to be melted are melted, pressure is applied to the tip of the stud and the section of the base material that has been melted, and the stud and base material are welded together after the current has been cut off.
In a well known method, a stud is brought into contact with a base material, voltage is applied between the stud and the base material, the stud is lifted slightly off the base material, an arc is generated between the stud and the base material, the tip of the stud and the section of the base material to be melted are melted, pressure is applied to the tip of the stud and the section of the base material that has been melted, and the stud and base material are welded together after the current has been cut off. In Japanese Utility Model Application Disclosure No. 5-49172 and Japanese Utility Model Application Disclosure No. 6-48967, a pilot arc with a small amount of current is generated, the main arc with a large amount of current is generated, the tip of the stud and the section of the base material to be melted are melted, pressure is applied to the tip of the stud and the section of the base material that has been melted and the stud and base material are welded together (the so-called drawn arc method). In automobile manufacturing, aluminum and aluminum alloy vehicle frames and bodies are also increasingly being used because of their lighter weight. In Japanese Utility Model Application No. 63-173583, a T stud consisting of a large-diameter head and a rod-shaped shaft is welded to a vehicle frame, and a clip for securing a member such as wiring is fastened to the T stud.
Technologies have already been developed to weld T studs to vehicle bodies and frames when the bodies and the T studs are made from iron-based metals. In these welding technologies, the T stud is welded to the body or frame while maintaining a constant level of strength. For example, when the iron-based T stud 1 in FIG. 1 has a 5-mm diameter head 2 and a 3-mm long, 3-mm diameter rod-shaped shaft 3, the height of the stud 1 below the neck after being welded to a base material 5 such as an iron-based body is about 2.6 mm, the reinforcing height (h) of the reinforcement 6 is less than 1 mm, and the diameter (d) of the reinforcement 6 is less than 5 mm. In this way, enough space remains on the shaft 3 of the molten T stud 1 to accommodate the clip disclosed in Japanese Utility Model Application Disclosure No. 63-173583, and attach the clip properly and securely.
However, this technology was developed to weld an iron-based T stud to an iron-based base material. When the base material of the body or frame consists of an aluminum-based metal such as aluminum or an aluminum alloy, it is difficult to weld an iron-based T stud to it. If a stud consisting of an aluminum-based metal such as aluminum or an aluminum alloy is welded in the same manner as an iron-based stud, the proper height below the neck, reinforcing height, and welding spot diameter cannot be reliably obtained. In addition, the strength after welding varies and a stable welding strength cannot be obtained. Therefore, the purpose of the present invention is to provide a stud welding method and device able to reliably obtain the desired welding profile and welding strength even when the stud is made from aluminum or an aluminum alloy.
In accordance with the present invention, a method of welding a stud is provided. In another aspect of the present invention, a welding system is provided for a weld stud. A further aspect of the present invention employs a weld stud with a substantially conical end section. Still another aspect of the present invention includes a welding method, wherein an aluminum or aluminum alloy stud is brought into contact with an aluminum or aluminum alloy base material, voltage is applied between the stud and the base material, the stud is lifted slightly off the base material, a pilot arc with a small amount of current is generated, the main arc with a large amount of current is generated, the tip of the stud and the section of the base material to be melted are melted, pressure is applied to the tip of the stud and the section of the base material that has been melted and the stud and base material are welded together, and the current is divided into stages and incrementally increased as the main arc is generated from beginning to end, and/or the molten tip of the stud is applied under pressure to the molten base material in under five milliseconds after the main arc current has been cut off.
The present invention also includes a welding device, wherein an aluminum or aluminum alloy stud is brought into contact with an aluminum or aluminum alloy base material, voltage is applied between the stud and the base material, the stud is lifted slightly off the base material, a pilot arc with a small amount of current is generated, the main arc with a large amount of current is generated, the tip of the stud and the section of the base material to be melted are melted, pressure is applied to the tip of the stud and the section of the base material that has been melted and the stud and base material are welded together, the current is divided into stages from beginning to end and incrementally increased as the main arc is generated, and/or the molten tip of the stud is applied under pressure to the molten base material in under five milliseconds after the main arc current has been cut off. As a result, the desired height below the neck in the stud after welding (L in FIG. 2) is reliably obtained, the welding strength is high, and the reinforcement height (h in FIG. 2) and the diameter of the melted section of the base material (d in FIG. 2) are kept within the proper range.
In another aspect of the welding device and method of the present invention, there are three steps and the main arc in the first step is a small-current arc effective at removing oil from the surface and surroundings of the section of the base material to be melted, the main arc in the second step is an intermediate-current arc for melting the tip of the stud and the section of the base material to be melted and for keeping the area of the section of the base material to be melted within a predetermined range, and the main arc in the third step is a large-current arc for melting the tip of the stud and the section of the base material to be melted into each other deeply. A further aspect of the present invention uses a T stud having a large-diameter head and a rod-shaped shaft, and the profile of the end of the shaft is conical with a flat tip. As a result, the arc is concentrated in the center, the reinforcement does not tilt to one side, and the height of the reinforcement is kept from getting shorter. A pilot arc is not absolutely necessary.
Still another aspect of the present invention includes a welding method, wherein an aluminum or aluminum alloy stud is brought into contact with an aluminum or aluminum alloy base material, voltage is applied between the stud and the base material, the stud is lifted slightly off the base material, an arc is generated, the tip of the stud and the section of the base material to be melted are melted, pressure is applied to the tip of the stud and the section of the base material that has been melted and the stud and base material are welded together, the current is divided into at least three stages and incrementally increased from the beginning to the end while the main arc is generated, and/or the molten tip of the aluminum or aluminum alloy stud is applied under pressure to the molten base material in under five milliseconds after the arc current has been cut off. As a result, an aluminum-based stud can be welded properly.
Similarly, in still a further aspect of the present invention, a welding device or system is used wherein an aluminum or aluminum alloy stud is brought into contact with an aluminum or aluminum alloy base material, voltage is applied between the stud and the base material, the stud is lifted slightly off the base material, an arc is generated, the tip of the stud and the section of the base material to be melted are melted, pressure is applied to the tip of the stud and the section of the base material that has been melted and the stud and base material are welded together, the current is divided into stages and incrementally increased from beginning to end as the arc is generated, and/or the molten tip of the aluminum or aluminum alloy stud is applied under pressure to the molten base material in under five milliseconds after the main arc current has been cut off. As a result, an aluminum-based stud can be welded properly.
Various embodiments of the present invention are advantageous over prior devices. For example, because the main arc current of the present invention is divided into stages and increases incrementally in this welding method, the welding area of the section of the base material to be melted is kept within the desired range when the tip of the stud is being welded to the section of the base material to be melted, the tip of the stud and the section of the base material to be melted are melted into each other deeply, and the heat introduced to the stud and base material remains constant. Because the tip of the stud is applied under pressure to the base material in less time and the short current is controlled during this time, the splattering of molten metal is reduced by the pinch effect (a phenomenon in which the large current flowing through the molten fluid constricts the fluid, the constriction reduces the flow and lessens the constriction, and the lessening of the constriction once again constricts the molten fluid). As a result, the desired height below the neck in the stud after welding (L in FIG. 2) is reliably obtained, the reinforcement height (h in FIG. 2) and the diameter of the melted section of the base material (d in FIG. 2) are kept within the proper range, and high welding strength is maintained. Additional advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.